Today reconstruction of the Old Cedar Bridge is well underway. Previously we looked at the history of the bridge and how we got to the final decision that the bridge will be restored. This article continues with the actual restoration and construction process.
The Nuts and Bolts of Restoration
When restoring an old structure. There’s a lot of philosophical issues and sometimes conflicting goals. You want something functional that will be cost effective to maintain.
The Foundations in the river turned out to in pretty good shape, and will for the most part be left as-is
The Piers and Abutments are not in good shape. Normally with historic restoration you attempt to save as much as practical. However in this case the outer layers of all the piers were peeling off. Saving a historic core in the middle while replacing the concrete on the outside would be technically challenging, and possibly even dangerous to workers while leaving no historic concrete visible. So the decision was made to completely demolish and replicate them, down to using wood boards as forms as was done in the old days to leave a distinctive, rough edge.
The Deck was in even worse shape. This is what led to the closure, and it continued to rot in place. Some photos show how you can see daylight through some of the decking members. Initial plans were to attempt to repair it, but it soon became evident it was a lost cause. The 2008 proposal was to use laminated wood planks that would be placed side to side, negating the need for steel stringers underneath the deck.
The current plan is to use a special, lightweight modern concrete with a completely redesigned joist and stringer system, . This replicates the original concrete deck, although the asphalt wearing surface will not be applied to save weight and as there is no engineering need. The new lightweight deck system will lessen the wear on the remaining historic, visible parts of the bridge, while still allowing bicycles and pedestrians and the occasional emergency or maintenance vehicle.
The Trusses by contrast are in pretty good shape. One of the chords on the bottom (where it was hit with salt spray) would be only 1% above the required safety factor, so the decision was made to replace it as part of the project rather than the probability of having to come back in the few years and do it anyway, requiring another closure and construction mobilization. Some of the diagonal bracing has been bent by being hit with vehicles; this is not a safety issue and they never bothered to fix them before, but they are being straightened now, as the report notes: “the site of bridge members in this state of distress could cause the public unnecessary concern”
The bridge never had lighting, and they are not adding it now. It was considered, but it was noted that “the refuge is closed after dark.” Obviously the east-west trails will be closed, but it’s an interesting point whether it will be legal to travel north-south across the river. The old bridge had an “Area Closed After Dark” sign on it, but it appears you can use the bridges without leaving city-owned property and the New Cedar Bridge has a light on it for the trail as well as spill from the roadway lights. At any rate there are no street lights on road south of the bridge and as poorly as Bloomington lights their streets, not a good idea to be riding around without a good bicycle light after dark anyway.
As far as color is concerned, we all know the bridge as a rusty brown, which is actually a good match for the painted brown new bridge as well as blending into the natural surroundings. However it will be returned to it’s original dark grey color.
See this beautiful railing from the Holmes Street Bridge in Shakopee?
The Old Cedar Avenue Bridge railing is nothing at all like this. In fact it’s nothing but the type of gas pipe you buy at Home Depot. The original bridge was way out in the sticks, so unlike those closer to the city, little thought was given to ornamentation, and as I mentioned in the last part they had no idea they were creating beauty instead of just transportation. This leads to some philosophical and practical issues. Normally you want to save as much of the original structure as possible, but a gas pipe in 1920 looks a lot like a gas pipe in 2016 and virtually all of it would have been replaced already due to collision damage. Note how nondescript and bent out of shape the railing is. Not surprisingly, no one bothered to keep good records as to when they had to go out and replace which small section of it.
Moreover, the original configuration doesn’t meet modern standards for bicycle and pedestrian facilities–it’s not high enough and there’s too much space in-between the rails. So the what’s being done is
- The existing railings will be scrapped entirely
- New railing is being assembled out of gas pipe and the top rail will be somewhat higher than the original
- Steel cable will be used in-between the gas pipe to reduce the spacing to meet standards. Steel cable is allowed for railings as long as it it not the topmost rail (on the Holmes Street bridge photo you can see a single cable was added to allow it to meet specs.
Even the nuts and bolts are thought of. The original bridge used rivets exclusively. Nowadays riveting is becoming a lost art, and is prohibited for certain structural parts. The plan is to use rivets on visible pieces where it’s allowed and on pieces fabricated in the shop. Button-Head bolts, which resemble a rivet from one side at least, will be used in other visible areas, and the contractor will be allowed to use standard hex-head bolts underneath the bridge where no one but the frogs will see it. Generally, the bolts will be mounted button head inward, due to both practical concerns with getting a wrench in tight places, and aesthetic as the inside side of the bolts will be viewed up close. This unavoidably alters the aesthetic slightly from the outside. Consideration was given to putting plastic caps on the outside, but they would still stick out more, and that would introduce an inappropriate material.
The Project Begins
The project initially got off to a rocky start. To begin with, CenturyLink had move a fiber optic cable that was in the way. Their boring machine broke, and it broke directly underneath a significant oak tree, which they were not allowed to cut down to retrieve it, so they had to bring in a new machine and start boring again from the beginning. The second task was the building of a temporary bridge in order to provide access.
Next demolition of the old bridge deck was done with small excavators removing the wood, an then the rotten steel was removed. Next massive cranes were brought in and shoring towers were built and an entire section of the bridge was lifted off the piers which is easier to do with no decking, only lightweight temporary bracing to keep it in shape. This is very impressive visually with the huge cranes dwarfing the bridge. While suspended the piers were being demolished and rebuilt and the gusset plates evaluated and replaced if needed. The bridge has now piers, and construction on the new deck is underway.
Going together with the long term plan to reopen the bridge and open the valley up to a wider demographic by filling in a gap in our paved trail network are plans to make the trial-head more functional and attractive, and even enable school groups to visit. Some invasive underbrush and non-significant trees are being cut down around the parking area. Significant canopy trees are being left. This will provide a more open, attractive, park-like atmosphere around the immediate parking area, and increase the perception of safety. (“Perception” being the term from the study, not mine). A mowed, maintained area for picnicking will be located between the bridge and the parking lot. A modern restroom and shelter building is being built just out of the floodplain on the east side of the street. A new boardwalk with rails has replaced the a rotting structure.
Earlier plans were to add nothing but a striped biked lane going uphill (northbound Old Cedar) and sharrows going downhill. The revised plan includes a fully protected eight to ten foot off road trail. This will be a city-owned extension of the Nokomis-Minnesota River Regional trail that now runs between the Minneapolis network and 86th Street, and also connects to the Nine Mile Creek Regional Trail. This is a challenging engineering feat, with wetlands on the east side and a steep slope on the west. Since you open up all kinds of issues by cutting into a slope, the trail will cross to the east side near the curve. Originally they were looking at a boardwalk, but now it’s apparent something more like a bridge will be needed.
As a side note, I arrived an hour into the meeting about the new trail, and was only the second person to sign in. Does Bloomington not care about bicycling because the off-road infrastructure is so poor (the Nokomis trail is the first off-road paved trail anywhere in the eastern half of the city), or is it so poor because Bloomington doesn’t care? Or do people just figure it was going to be built anyway, and are not interested into finding out more in advance or providing input? I do know that public meetings aren’t the best gauge of public opinion, they tend to skew towards older people with more time on their hands, and people really involved in the community (the previous name I recognized as a regular contributor to the East Bloomington Residents Facebook Group). At least I got plenty of time chatting with the city engineer about this and other projects.
Finally, back to the bridge: the informal name is now official; the Long Meadow Bridge is now the Old Cedar Bridge.
Minnesota Statute 161.14 Subd 77: Minnesota state bridge number 3145, the Camelback bridge over the Minnesota River overflowage (referred to as Long Meadow Lake) constructed in 1920, is designated and named the “Old Cedar Avenue Bridge.” This designation and name also applies to any renovation or reconstruction of the bridge and must be used in any publicly financed signage that refers to the bridge.
I can’t help feel excitement for all the improvements coming to the river valley, and I look forward to being there on opening day with my camera and bicycle to be one of the first to ride across the old/new bridge. Yes, it was expensive, but sometimes nice things cost money and this was money well spent.